if (OpenMP)

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Specifies whether a loop should be executed in parallel or in serial.

if
(expression)  

where,

expression
An integral expression that, if it evaluates to true (nonzero), causes the code in the parallel region to execute in parallel. If the expression evaluates to false (zero), the parallel region is executed in serial (by a single thread).

if applies to the following directives:

• parallel

• for

• sections

For more information, see 2.3 parallel Construct.

// omp_if.cpp  
// compile with: /openmp  
#include <stdio.h>  
#include <omp.h>  
  
void test(int val)  
{  
    #pragma omp parallel if (val)  
    if (omp_in_parallel())  
    {  
        #pragma omp single  
        printf_s("val = %d, parallelized with %d threads\n",  
                 val, omp_get_num_threads());  
    }  
    else  
    {  
        printf_s("val = %d, serialized\n", val);  
    }  
}  
  
int main( )  
{  
    omp_set_num_threads(2);  
    test(0);  
    test(2);  
}  

val = 0, serialized  
val = 2, parallelized with 2 threads  

Clauses